Fourth seed Agnieszka Radwanska of Poland withdrew from the Western and Southern Open for personal reasons on Thursday, sending defending champion Li Na of China through to the semi-finals.
Radwanska had earlier beaten Russian Elena Vesnina 6-0 6-2 to advance to the quarter-finals but withdrew from the tournament to attend her grandfather's funeral.
"I'm very sorry that I have to withdraw from the tournament. Unfortunately, my grand-dad passed away last Sunday," said Radwanska in a statement.
"The funeral is going to be Saturday and I need to be there.
"I am disappointed to not continue with the tournament, especially because of my form so far this week.
"It was a difficult decision, but I need to be go home and be with my family."